Overwind preventer



Patented Nov. 11, 1952 UNITED STATES PATENT OFFICE OVERWIND PREVENTERFoster H. Brown, Brooklyn, N. Y.

Application December 31, 1948, Serial No. 68,630

9 Claims.

This invention relates to main-spring barrel assemblies, especiallythose used in watches. It is, however, equally appropriate to any otherdevice, horological or not, employing a main-spring barrel.

The majority of jeweled watches are now provided with mainspring-drumchambers smaller than a five-grain aspirin tablet, i. e. less thanthree-eighths of an inch in diameter.

It is obvious that, if any watch is forced beyond full-wound conditionwhile being wound, some part may rupture.

Devices heretofore proposed are, basically, internal brake mechanismswith contracting shoes. They are designed and constructed so that asection or sections of the shoe or band can be contracted and pulledaway from contact with part or parts of the drum-wall surface by theaction of the radial components of the power of the mainspring. In otherwords, this functional movement decreases the size of the band, thusreducing the amount of static friction or holding power between the bandand the drum wall. In use, this action continues until the holding powerof the band is overcome by the power of the mainspring, at which timethe band slips.

The present invention is also, basically, an internal brake mechanism,except that, unlike the prior art, its shoe or band does not contract orreduce its traction.

An object of the present invention is to provide an efiicient safetybarrel mechanism, the shoe of which is of equal radius and cross-sectionin all its parts and, to all intents and purposes, remains in onehunderd per cent contact with the barrel wall under all conditions andat all times.

A further object is to provide a barrel clutchband construction withoutany torque-producing characteristics whatsoever and to provide a surfacefor the mainspring which, to all intents and purposes, is equal to thesurface of a naked barrel wall, hence eliminating any possibility ofincreasing inter-coil mainspring friction and allowing the mainspringunrestricted functional freedom at all times.

A further object of this invention is to provide a mainspring-barrelclutch which has an established and non-varying kinetic frictionalfactor higher than the full torque of the mainspring, thus eliminatingany and all leaping tendencies or characteristics which the shoe bandmight have.

Another object of this invention is to provide a barrel-clutch bandwhich can be easily inserted in, removed from, or reinserted in, thedrum, or replaced, independently of the mainspring.

A further important object of this invention is to provide, by means ofthe substantial difference in the feel of the winding tension, a silent,smooth and commercially acceptable full-wound signal. Such a signal isprovided by the clutch in accordance with the invention when it goesinto action.

In accordance with the present invention, these objects are accomplishedby providing a clutch, the inner member of which is made of mainspringstock having a length such that, when inserted within the outer member(the barrel or mainspring housing), its ends abut and it forms,virtually, a continuous and concentric circle. This end-to-end jointure,plus the fact that the said inner member is preferably constructed fromthe same material as that of its associated mainspring, results in aclutch-shoe construction which occupies the same amount of space as isoccupied by a single layer of mainspring stock.

This construction is also advantageous in that it is applicable toconventional mainsprings and housings. The only basic requirement is ahookless barrel. The clutch design is such that it can be easilymanufactured, and its cost is less than that of many currentmainspring-to-barrel connections.

The clutch is particularly adaptable for use to prevent damage caused byoverwinding, such as a ruptured spring, or, in the event that the springdoes not break from the overwinding, to prevent the excessive tensionfrom causing damage to the associated mechanism, such as twisting offthe stem, damaging or breaking teeth of one or more gears, or otherdamage. In the event that the main-spring should break because of inerent characteristics, the clutch yields to the shock and tends toprevent the possibility of resulting damage. The fact that the clutchrequires only a small amount of space, is a most important advantage,particularly in wrist watches, in which the main-spring barrel is oftenone-quarter of an inch or less in diameter. Such barrels are. in fact,Lilliputian power houses.

Other obj cts and further advantages 0* the invention will becomeapparent from the following description and from the accompanyingdrawings which show, by way of example, several embodiments of theinvention.

In the drawings,

Fig. 1 is a frOnt view of a barrel assembly, including a clutch inaccordance with my invention, the barrel cover being removed to show theinterior of the barrel.

Fig. 2 is a cross section taken approximately on the line 22 of Fig. 1,with the cover in pla e.

Fig. 3 is a View similar to Fig. 1, but showing another embodiment ofthe invention in which the peripheral wall of the barrel is tapered, orfrusto-conical.

Fig. 4 is a cross section taken approximately on the line 44 of Fig. 3.

Fig. 5 is an edge view of the clutch shoe removed from the main-springassembly of Fig. 3.

Fig. 6 is a view of the inner face of the clutch shoe shown in Fig. 5.

Fig. 7 is a view similar to Fig. 5 but showing another form of clutchshoe.

Fig. 8 is a face view of the clutch shoe shown in Fig. 7.

Fig. 9 is a fragmentary edge view of the clutch shoe and a connectingmember in accordance with another modification.

Fig. 10 is a fragmentary view similar to Fig. 9 showing still anotherembodiment.

Fig. 11 is a graph showing the relation between the torque and the turnsof a characteristic mainspring as the spring is wound up and thenallowed to unwind.

A main-spring assembly as shown in Figs. 1 and 2 of the drawings,comprises a housing, drum or barrel I, an arbor 2, a main-spring 3, anda clutch shoe 4, the latter being, in accordance with the presentinvention. While the particular mainspring barrel assembly illustratedin the drawings is intended for use in a watch, the invention is alsoapplicable to clocks and other spring driven devices, and as beforestated, to other types of barrels. It will be understood that themainspring assembly for a watch is actually very much smaller than shownin the drawing. In a pocket watch the diameter of the barrel may be fromone half to three quarters of an inch, while the barrel of a wrist watchmay be one quarter inch or less in diameter. The assembly is shown on anenlarged scale in the drawings for greater clarity.

The housing or barrel I may be formed of' any suitable material such asmetal or plastic and comprises a back or bottom wall II, an annularperipheral wall I2 and av removable cover I3. The cover I 3 snaps intoplace against an annular shoulder I4 provided on the inside of theperipheral wall I2, being normally held in place by the resilience andfrictional contact of the barrel and the cover. The barrel wall I 2 hasa circular inner surface which is utilized for engagement by the clutchmember 4.. The barrel shown in the drawings by way of example is a goingbarrel provided with a series of teeth around its periphery for. drivingthe succeeding member of the device. The bottom Wall I I and the coverI3 are provided at their centers with alignedv circular Openings. toreceive the arbor 2.

It should be here noted that the examples shown are not intended tolimit this invention to going barrels alone. The word barrel is meant toimply any housing construction suitable for a barrel assembly.

The arbor 2 has circular bearing surfaces 2I and 22 adapted to engagethe holes in the bottom wall II and the cover I3 of the barrel.Intermediate the bearing surfaces 2| and 22 the arbor has a cylindricalportion 23 of enlarged diameter about which the main-spring 3 is adaptedto be Wound. One side of the cylindrical portion 23 is preferablyflattened, as indicated at 24 (Fig. l) and provided with a hook 25adapted. to engage a slot or hole in the inner end of the main-spring toconnect the main-spring. with the arbor. It will be understood thatother suitable connecting means may be used. The ends of the arborproject beyond the bottom wall I I and the cover I3, respectively, andare provided with pivot or bearing portions 26 and 27, respectively, forrotatably mounting the arbor in suitable bearings. One end of the arbor,usually the end that projects through the bottom wall II, terminates ina non-circular or squared end portion 28 which provides for a drivingconnection with suitable winding mechanism for the main-spring 3. A pawland a ratchet wheel (not shown) are customarily associated with eitherthe arbor or the winding mechanism to hold' the POW?!) 95 $11main-spring after it is wound.

The main-spring 3 is formed of a strip or ribbon of tempered springsteel, or. a suitable alloy, which is wound in spiral form about thearbor 2. In Fig. 1 the inner end 3I of the main-spring is attached tothe arbor, for example, by the hook 25, while the outer end 32 isconnected with the clutch shoe 4, as will be more fully described below.The width of the main-spring is slightly less than the distance betweenthe bottom wall I I and the cover I3 of the barrel, so that themainspring fits in the barrel without binding edgewise. The length andthickness of the main-spring are preferably such that the springoccupies approximately half of the free area inside the barrel, i. e.,the area between the arbor and the peripheral wall formed by the insidesurface of the clutch shoe. In Figs. 1 and 2 the main-spring is shownfully wound, in which condition it is closely Wrapped around the arbor2. As the main-spring runs down its turns or coils gradually expand andseparate from one another. When the mainspring is fully run down,itscoils or convolutions have expanded and lie one against the otherinside the periphery of the clutch. As. will be more fully explainedbelow, a feature of the present invention is. that the clutch shoe 4does not appreciably decrease the space available for the main-springand it providesa smooth, concentric, circular wall for the spring at alltimes.

The clutch shoe. 4, in accordance with the present invention, is made ofa strip or ribbon of spring stock. The width of the strip issubstantially equal to thewidth of. the inner surface of the peripheralvwall. I2 between the bottom II and the cover I 3 of the barrel. Itslength is substantially equal to the inner circumference of theperipheral wall I2. Its thickness is of the same order as the thicknessof the main-spring, as will be more fully explained. below.

In its relaxed condition, before it is put into the barrel it may bestraight, as shown in Fig. '7, or curved, as shown in Fig. 5, the radiusof curvature being greater than the radius of the barrel. Alternatively,the clutch shoe may be reversely curved, or it may have the end portionscurved in one direction. The opposite ends M are substantially square,although the corners are preferably slightly rounded, as shown in Fig.6, and/or the ends 4| are toed-up slightly, as indicated in Fig. 7,sothat there is no tendency for the clutch shoe ends to dig into thebarrel wall. This further improves its action.

In inserting the clutch shoe in the barrel, it is preferably coiled intoapproximate circular shape with the ends overlapping and slippededgewise into the barrel. The clutch ring is then spread and the endsare snapped into abutting relationship, so that they press against oneanother in a flush-butt joint. to maintain. the circularity of the shoeand hold it in. contact with the barrel wall throughout itscircumference. This construction produces novel and surprising results.The thin clutch shoe now develops its own tension, which is utilized toproduce the resulting eificient traction, and in addition, the shoe nowcan never upset the normal main-spring torque. If a somewhat shorterclutch shoe were used, the opposite ends would. meet at an angle some-What: like the apex of a. heart. In other words, the adjacent endportions of the clutch shoe would tend to straighten out and extendsomewhat chordwise across corresponding sectors of the circle formed bythe peripheral wall of the barrel. However, in accordance with thepresent invention, thfi length of the clutch member 4 and the pressureof the abutting ends 4| are such that the clutch member is held incircular form substantially corresponding to, and in contact with, theinner periphery of the barrel wall l2 throughout its entire innercircumference. The barrel shoe maintains this concentricity and its truecircular shape at all times. The outside surface of the clutch or barrelshoe being substantially equal in area to the inside surface of theperipheral wall of the barrel, and the shoe being therefore in contactwith the barrel throu hout its entire periphery, the maximum area oftraction and frictional engagement is thereby provided. The barrel shoemaintains this substantially 100% bearing surface at all times.

The outer end of the main-spring 3 is attached to or connected with theclutch member 4 in any suitable manner. In the form illustrated in Figs.1, 2, 5 and 6, the clutch member 4 is provided with a punched-out orextruded hook 43 which engages a hole with which the outer end of themain sprin is provided. In the form shown in Figs. '1 and 8 the clutchmember 4 is provided with a hole 44 which is adapted to be engaged by ahook provided on the outer end of the main-spring.

When the outer end of the main-spring is connected directly to theclutch member 4, as in Figs. 1 and 2, the point of connection ispreferably placed at least a short distance from the abutting ends 4| ofthe clutch shoe so that there is no tendency for the clutch-shoe ends toseparate or for the end to which the main-spring is connected to bepulled away from the barrel wall by the radial component of the pull ofthe mainspring when the spring is fully wound.

Preferably, the point of connection is in the trailing or rear half ofthe clutch shoe so that the major portion of the shoe is pushed ratherthan pulled around the inner periphery of the barrel by the main-spring,the direction of movement being as indicated by the arrow a. The pushingaction also provides a self-energizing eifect which increases theslipping resistance or traction of the clutch. In other words,considering the direction of rotation of the clutch, the outer end ofthe main-spring is preferably connected to clutch member 4 at a point atleast a short distance ahead of the abutment. By virtue of thisarrangement the major portion of the shoe is pushed and tends to expandunder the influence of the main-spring, and the clutch thereby tends tobecome self-energizing.

The outer end of the clutch member 4 and the inner surface of theperipheral wall [2 of the barrel are smooth. It should be noted herethat the clutch and the main-spring are lubricated in any mannerappropriate for the main-spring itself. The slipping resistance of theclutch, or in other words, the torque that will be held by the clutchwithout slipping, can be varied by varying the pressure with which theopposite ends 4| of the clutch member 4 abut one another. This, in turn,is determined by the length of the clutch shoe in relation to the innercircumference of the barrel wall, and also by its relative thickness.

Because of the inherent characteristics of the thin flexible clutchshoe, it closely hugs the barrel wall surface, conforming to it inshape, and thereby, in resisting movement, provides maximum traction oradhesion between itself and the housing wall. It has been found that aclutch shoe approximately half the thickness of its associatedmain-sprin functions satisfactorily and is sufficient to hold fullmain-spring torque in self-winding timepieces, as in these no signal isrequired, or even desirable. In other cases, where a strong signal isdesirable, it has been found that a slight increase in the thickness ofthe clutch shoe relative to its main-spring thickness adds considerablyto its holding power, all other dimensions remaining the same. In fact,these barrel shoes can be made so tight that they never slip. It holdsits original traction value indefinitely and in its preferred form isself-energizing.

In production manufacturing, desired traction or pressure can be assuredmerely by adhering to usual precision methods in the making of theparts. In fitting a clutch shoe to an individual barrel, it ispreferably made slightly longer than the calculated length and either orboth ends may then be trimmed off slightly until the shoe fits with justenough tightness to provide the desired traction.

Fig. 11 is a graph illustrating the operational characteristics of atypical main-spring. The abscissae of the curve w represent turns of themember of the barrel assembly through which the spring is wound, and theabscissae of the curve 11. represent turns of the member of the assemblythrough which the mechanism is driven. The ordinates indicate theproportionate amount of torque at various stages between fully wound andfully unwound. The upper curve w represents the torque required to windthe mainspring, while the lower curve it represents the torque deliveredby the main-spring in unwinding. The point ;f on the curve w representsthe point at which the mainspring is fully wound. At this point thecoils of the mainspring are adjacent one another, being compactly woundaround the arbor 2, as illustrated in Fig. 1. Up to the point I, thetorque has gradually increased, as indicated by the curve w. Furtherwinding of the main-spring starts to pull its outer end away from thebarrel, as shown at 32 in Fig. 1, and the torque increases at a rapidrate, as indicated by the dotted portion 0 of the curve w, representingoverwinding of the main-spring. The point B represents the approximatepoint at which the mainspring will rupture or some part of theassociated mechanism will give way if the overwinding is continued.

The holding power, traction, or slipping point of the clutch ispreselected, as indicated above, so as to hold the torque of the fullywound mainspring, and preferably slightly more. Hence, the clutch willnot slip until the main-spring is fully wound, but will slip before thespring or some other part of the mechanism breaks or is damaged.Preferably, the holding power of the clutch is slightly more than themaximum power of the mainspring, so that the traction of the clutch canbe felt by a person winding the mainspring, thus giving a clearindication or signal that the spring is fully wound. While latitude ispermissible in the selection of the slipping point, it should be betweenthe points 1 and B on the curve w shown in Fig. 11, and preferably inthe lower half of the range. The slipping point has been indicated, byway of example, on the curve 10, at point S. After the slipping point ortraction of the clutch has been established by properly selecting thematerial and determining the dimensions of the shoe or inner member 4,it will retain its value indefinitely. When the slipping point of theclutch is reached, it creeps or slips silently and smoothly, and at thesame rate at which the mechanism is overwound. As the slipping point ortraction value of the clutch is greater than the maximum torque of themain-spring; full main-spring power-is held, and an unmistakable andcommercially acceptable signal is provided. This is of particularimportance in timepieces or other small mechanisms, as it is essentialfor the main-spring to be wound fully and for the full power of themainspring to be held in order that the mechanism can run satisfactorilyfor the prescribed period of time. 7

In winding and operating tests made with several conventionalself-winding or automatic timepieces, havinga 72-tooth barrel driving a12-tooth center pinion and providing six hours of running time perbarrel revolution, it. was found that using the original drag units andmain-springs, the main-spring assemblies were able,,on the average, todevelop and store sufficient main-spring energy to drive the barrel fromfour, to five revolutions. Further tests made with the same barrels, butsubstituting clutch shoes according to this invention, and appropriatelylonger main-springs, made possible by the lesser space requirements ofthe clutch, showed an average development of over six driving turns. Itshould be particularly noted that this extra reserve power is alwaysadded to the most favorable portions of the power curve, that is, to thetop. This invention, on each full winding, thus provides a gain in someof these examples of as much as two full turns of favorable reservepower, or twelve hours of additional running time, thereby doubling thelength of the most desirable section of the power curve.

A clutch in accordance with this invention does not appreciably changethe generally accepted proportions for a correctly proportioned hoerological barrel assembly.

The operating characteristics of a main-spring, and in particular, theuniformity of its torque curve, do not depend entirely on the dimensionsof the barrel. The uniformity of power flow, however, depends somewhaton the material from which the spring is made, its dimensions,proportions, hardness and resiliency. If the mainspring is too soft, itsets (becomes permanently deformed in use) and loses much of its power.As a general rule, the desirable characteristics of a spring increasewith an increase in hardness. Therefore, since clutch member 4 is notsubjected to repeated flexing or bending it can be relatively hard, andhardness of this member is desirable because it increases the tractionand general efficiency of the clutch, all other things remaining equal.

The embodiment of my invention shown in Figs. 3 and 4 is similar in mostrespects to that shown in Figs- 1 and 2, and corresponding parts aredesignated by the same reference numerals. There. are, however, twoprincipal differences. The first is that the inner peripheral wall ofthe barrel. slopes slightly, being of greater diameter adjacent thebottom wall H. The second is in the method of connecting the main-springwith the clutch.

As will be seen in Fig. 4, the inner surface of the peripheral wall [2of the barrel is frustroconical rather than cylindrical", as shown inFig. 2. The larger diameter of the chamber is at a point adjacent thebottom wall H of the barrel. The inclination of the wall is slight,being, for example, from one to five degrees to the axis of the barrel,and preferably about two degrees. The" flexible clutch member 4 adopts acorrespending shape so as to conform with the inner surface of theperipheral barrel wall It, and, when the clutch slips from time to timein preventing overwinding of the main-spring, due to this novel design,the shoe always tends to hunt toward, and therefore remains at, thebottom of the barrel. An inclined barrel wall also makes it practical touse a clutch in coverless or open barrel constructions.

The connection between the main-spring and. the clutch member l in theembodiment of Figs. 3 and 4 is provided by a tongue or pushed link 5|.One end of the link 5| engages a hook 52 provided at the outer end ofthe main-spring. The other end engages a hook or projection 4-3 providedon the inner face of the clutch member 4, for example, by being stampedout of the clutch member itself (Fig. 3). The link 5| is preferablyarcuate, as shown, in order to conform with the curvature of themain-spring and the clutch shoe whenthe main-spring is fullyrun down.The link 5|, and for that matter, any tongue end, permits the outer endof the main-spring to move inwardly and away from the barrel wall, hencetending to augment the pressure of the clutch member 4 as themain-spring is wound up. It has the further advantage of avoiding anytendency of the mainspring to pull inwardly on the clutch member 4 whenthe spring is tightly wound. By reason of this fact, the point ofconnection between the link El and the clutch memher 4 with respect tothe abutting ends 4! of. the clutch member, is not as critical.

Figs. 9 and 10 show still other means of conneeting the main-spring withthe clutch member. In Fig. 9, a novel type of brace 5| is riveted to theclutch member 4 as indicated at 53. The opposite end of the brace 51engages a hook 52 on the outer end of the main-spring, as for example,in Fig. 3. The push brace 5i is sufficiently flexible to allow the outerend of the main-spring to move inwardly and away from the peripheralwall formed by the clutch shoe as the spring is wound up. Braceconstructions are favored by some horological engineers, as they tend tohold the unwinding main-spring more concentric. thus tending to reducefriction between the main-spring coils as they unwind. Fig. 9 shows thebrace in the relative position it assumes when the main-spring is nearlywound up.

In the embodiment shown in Fig. 10, one end of the tongue 5i is rivetedto the outer end of the main-spring, as indicated at 54. The oppositeend of the tongue engages a hook 43 provided. on the clutch member 4.Tongue-ended main-springs are extensively used and readily obtainable.The clutch in accordance with the present invention is thus readilyapplicable to use with standard types of main-springs.

It will. be understood that the various features shown in the severalfigures are mutually interchangeable in any suitable barrel assembly.For example, the means for connecting the mainspring with the clutchmember shown in Figs. 3, 9 and 10 can also be used in the embodiment ofFigs. 1 and 2. Likewise, the main-spring and clutch member shown inFigs. 1, 2, 5 and 6, as well as the clutch member shown in Figs- 7 and 8may be used with. an inclined barrel wall, as illustrated in Figs. 3 and4.

Many additional advantages other than those heretofore mentioned will bereadily apparent tothose skilled in the art.

For example, where more than one barrel assembly is used in a singledevice, with the arbors geared to a single winding key, this inventioneliminates both the risk of one short mainspring taking all the windingstrain and the need of setting up equally, and, in use, should eithermain-spring lose a turn, the equal tension of both is simplyre-established as turning the winding key and thereby slipping thetighter spring by means of the clutch brings the lesser tensioned Springup to full tension, at which point they are equalized, even ifinadvertently improperly synchronized when first set up.

Still other desirable applications and modifications will be apparent tothose skilled in the art within the scope of the invention claimed.

I claim:

1. A main-spring assembly comprising a barrel having an annular wall, amain-spring within the barrel, an arbor for engaging the inner end ofthe main-spring, a clutch member for operatively connecting the outerend of the mainspring to the barrel, and means for connectin the clutchmember with the said outer end of the main-spring, said clutch memberadapted to fit in place within the barrel between the barrel and themain-spring and being formed of a single turn of material with its endsin flush abutting relationship and being of a length to exercise apressure against the barrel wall.

2. A main-spring assembly comprising a barrel having an annular wall, amain-s ring within the barre an arbor for engaging the inner end of themain-spring, and a clutch for operatively connecting the other end ofthe main-spring to the barrel, said clutch adapted to fit in placewithin the barrel between the barrel and the main-spring and beingformed of a single turn coil with its ends abutting and flush with oneanother, and having projecting means thereon for engagement with thesaid other end of the main-spring.

3. A mainspring assembly comprising a barrel having an annular wall, amainspring within the barrel, an arbor for engaging the inner end of themainspring, and a clutch for operatively connecting the other end of themainspring to the barrel, said clutch adapted to fit in place within thebar rel between the barrel and the mains ring and being formed of a sinle turn coil with its ends abutting and flush with one another andhaving an aperture therein adapted to be engaged by a projecting meanson the said other end of the mainspring.

4. A mainspring assembly comprising a barrel having an annular wall, amainspring within the barrel, an arbor for engaging the inner end of themainspring, a clutch for operatively engaging the barrel, said clutchadapted to fit in place within the barrel between the barrel and themainspring and being formed of a single turn coil with its ends abuttingand flush with one another and readily disconnectible means operativelyconnecting the other end of the mainspring with the clutch member at apoint spaced from the end of said member.

5. A mainspring assembly comprising a barrel having an annular wall, amainspring within the barrel, an arbor for engaging the inner end of themainspring, a clutch for operatively engaging the barrel, said clutchadapted to fit in place within the barrel between the barrel and themainspring and being formed of a single turn coil with its ends abuttingand flush with one another and a push link operatively connecting theother end of the mainspring with the clutch member.

iii

6. In a mainspring assembly the combination with a barrel having anannular wall and a mainspring within said barrel, of a clutch membercomprising a strip of spring material of substantially the samecross-section and characteristics as that of the mainspring and of alength substantially equal t the inside circumference of said annularwall, said member bein connected with one end of the mainspring andbeing fitted within said wall with its ends abutting and flush with oneanother to hold said member in frictional contact with said wallthroughout substantially its entire circumference and provide asubstantially constant resistance to slipping appreciably greater thanthe maximum torque of said spring.

'7. In a mainspring assembly, the combination with a barrel having aside wall and an annular wall having a frusto-conical inner surface withthe larger diameter adjacent said side wall, and a mainspring in saidbarrel, of a clutch member com rising a strip of spring material havinga length at one side edge substantially equal to the maximum internalcircumference of said annular wall and a length at the other side edgesubstantially equal to the minimum internal circumference of saidannular wall, said strip being connected with one end of said mainspringand being fitted in said barrel with its ends abutting in a flush buttjoint t maintain substantially the entire outer surface of said strip incontact with the inner surface of said barrel.

8. In a mainspring assembly. the combination with a barrel having a sidewall and an annular wall having a frusto-conical inner surface with itslarger diameter adjacent said side wall and a mainspring in said barrel,or a clutch member readily detachably connected with the outer end ofsaid spring and comprising a single turn of resilient strip materialfriction-ally engaging the inner surface of said annular wall and havingits ends meeting in a single thickness fiush butt joint.

9. A mainspring assembly comprising a barrel having an annular wall, amainspring within the barrel, an arbor for engaging the inner end of themainspring, a clutch member for operatively connecting the other end ofthe mainspring to the barrel, and means for connecting the clutch member with the outer end of the mainspring, said clutch member adapted tofit in place within the barrel between the barrel and the mainspring andbeing formed of a single turn of material with its ends in flushabutting relationship and being of a length to form a substantially truecircle.

FOSTER H. BROWN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 397,504 Karthaus Feb. 12, 1889448,191 Fasoldt Mar. 10, 1891 497,429 Jobson May 16, 1893 1,091,561Carlstrom Mar. 31, 1914 1,52 .0' 3 Odom Jan. 6, 1925 1,619,943 LehwessMar. 8, 1927 1,962,056 Colomb June 5, 1934 FOREIGN PATENTS NumberCountry Date 145,733 Switzerland May 16, 1933

